In general, after being mixed into an aqueous or solventborne resin system, an organic pigment must be further dispersed prior to its final application. This additional dispersion step generally requires that the pigment be dispersed for a period of 2 to 48 hours using milling equipment, such as a vertical or horizontal ball mill or an attritor mill with milling media, such as glass beads or stainless steel balls. Since this additional dispersion step is both time consuming and costly, the elimination of this step by using pigments that are adequately dispersed during a simple mixing step, herein referred to as stir-in pigments, is a great advantage.
A number of effect pigments are stir-in pigments which can be added to a coating or ink system without an additional dispersion step. In this application, the expression "effect pigment" means inorganic or organic pigments which show metallic, pearlescent and/or silky-luster effects. Such effect pigments are generally inorganic pigments such as metallics, like aluminum, TiO.sub.2 -coated mica pigments, platelet graphite and platelet molybdenum disulfide. Other effect pigments are prepared by coating a flaky crystalline form of a substrate with a small amount of a dyestuff or pigment, for example, a metal oxide coated mica. In addition, the effect pigments include certain platelet-shaped organic pigments, such as platelet copper phthalocyanine and those described in U.S. Pat. No. 5,084,573, U.S. Pat. No. 5,095,122, and allowed U.S. patent application Ser. No. 08/013,444. However, no non-platelet-shaped organic stir-in pigments are described.
U.S. Pat. No. 5,298,076 discloses the use of carbazole dioxazine crude of particular particle size and specific surface area as a multi-colored effect pigment for use in a variety of applications, including as a stir-in pigment. However, this publication does not suggest that other pigment crudes could be utilized as stir-in pigments.
The present invention relates to the general discovery that organic pigments having particles with an average particle size within a specific range are useful as stir-in pigments. The invention further relates to the discovery that the range is somewhat broader if the organic pigment is combined with an inorganic filler to form a pigment composition.
Since the effect pigments that can be used as stir-in pigments are generally used in conjunction with very small particle size transparent organic pigments in the preparation of effect coatings, an additional dispersion step is necessary to prepare such coatings due to the presence of the aggregated, small-particle-size organic pigment. However, if the effect pigment is used in conjunction with a stir-in organic pigment or a pigment composition of the present invention, the costly additional dispersion step is avoided.
The inventive pigments and pigment compositions have an additional advantage over the small-particle-size organic pigments in coating and ink systems because relatively increased concentrations of the inventive pigments and/or pigment compositions do not adversely effect the viscosity behavior and gloss of the coating or ink system. Thus, the inventive pigments and pigment compositions are formulated into coating and ink systems using reduced amounts of organic solvents.
In addition, the inventive pigments and pigment compositions exhibit an excellent flop effect and in certain cases a silky effect. The term "flop effect" is generally used in this application to describe an effect wherein different color shades or hues are observed when viewing a pigmented object from different viewing angles.
Thus, the inventive pigments and pigment compositions are valuable because they are utilized as stir-in pigments, have excellent rheological and gloss properties and demonstrate an excellent flop effect.